Cygnus Recoverable SSTO Rockets (15 to 600 tons)

[goldenpsp]

I open airbrakes in space, when I do my deorbit burn. I even stage all the chutes in space. Then warp to atmos and physic *4 to speed things up. I only come to *1 before chutes opens (around 8km).

Dumb question : did you jettisson the test payload ? (BTW, one time I nearly crash into the test payload which scratch the pain and rip off one of the airbrakes. That was close...)

I don't remember having lost an airbrake on any of the RR models. Even when I landed a RR100 with only 2 airbrakes because I misplaced the other 2. Sure they overheat, but never to the red zone.

Except for airbrakes, is there a specific part that seems to overheat ? On the first design I used a rocakmax adapter at the bottom. It used to overheat even with a heatshield. Only that part blew up (but the control probe was on the other side, so I lost the rocket. I removed this adapter and used a double heatshield. That went well until I used the bigger probe core so I didn't need the 1.25m stuff anymore. In the current configuration, I'm not even sure I need a heatshield.

BTW, The rocket you try to land don't have heathshield, but 7 engines.

Yes jettisoned the payload. I staged all the chutes as well. I will try leaving the airbrakes opened.

As I had mentioned everything seems fine until around 19km. Some parts show some heat but otherwise are fine. Around 19km very suddenly all of the engines get the overheat bar and explode, taking the rest of the craft with it. I can record a video if you want to see. I don't run any mods that change stock aerodynamics (like FAR or realchutes).

[Warzouz]

I'll recheck that and especially my game parameters.

Have you tried another rocket ?

[goldenpsp]

I'll recheck that and especially my game parameters.

Have you tried another rocket ?

I haven't. I will try some of the others however.

- - - Updated - - -

Ok update. I'm not sure if it was opening the airbrakes from the beginning and just trusting they aren't going to explode, or high physics warp causing less heat, but my last test run was a success.

thanks for the tips.

[Warzouz]

Hmmm, I'll check that too... I do the warp not to reduce heat but to save time !

[goldenpsp]

Hmmm, I'll check that too... I do the warp not to reduce heat but to save time !

I'm not positive that it does, but it "seemed" like the overall heat level was lower while I was timewarped.

[Sharpy]

I have tried opening airbrakes at different points in the descent. They overheat quickly so I tended to close them back up before they exploded

The only way to prevent them from overheating is to slow down to a safe speed... by keeping them open. All the way from 70km up to the ground. Keep periapsis at 48-50km. If you're entering from a to fast orbit it will simply eject you back into space. If you're coming in slow enough, you'll deorbit. It may not give you a KSC landing but it will give you a landing in one piece.

[Warzouz]

With RR125

Test 1a

LKO = 80km, 60m/s deorbit. Airbrakes open in space. No physical warp. All Chutes deloyed : Highest critical temp is airbrakes 1300K/2000K around 22km, then rapidly cooling down. No blowing up. (overshoot KSC by 50km)

Test 1b

LKO = 80km, 70m/s deorbit. Airbrakes open in space. No physical warp. All Chutes deloyed : Highest critical temp is airbrakes 1300K/2000K around 22km, then rapidly cooling down. No blowing up (too short, hit mountains).

Test 2

LKO = 80km, 60m/s deorbit. Airbrakes open at 30km. No physical warp. All Chutes deloyed : Highest critical temp is airbrakes 1300K/2000K around 20km, then rapidly cooling down. No blowing up.

Test 3

LKO = 80km, 60m/s deorbit. No airbrakes. No physical warp. All Chutes deloyed : Highest critical temp is airbrakes 1300K/2000K around 20km, then rapidly cooling down. No blowing up but chutes destroyed : crash.

I don't know what you did I didn't do, but I don't blow up.

[goldenpsp]

With RR125

Test 1a

LKO = 80km, 60m/s deorbit. Airbrakes open in space. No physical warp. All Chutes deloyed : Highest critical temp is airbrakes 1300K/2000K around 22km, then rapidly cooling down. No blowing up. (overshoot KSC by 50km)

Test 1b

LKO = 80km, 70m/s deorbit. Airbrakes open in space. No physical warp. All Chutes deloyed : Highest critical temp is airbrakes 1300K/2000K around 22km, then rapidly cooling down. No blowing up (too short, hit mountains).

Test 2

LKO = 80km, 60m/s deorbit. Airbrakes open at 30km. No physical warp. All Chutes deloyed : Highest critical temp is airbrakes 1300K/2000K around 20km, then rapidly cooling down. No blowing up.

Test 3

LKO = 80km, 60m/s deorbit. No airbrakes. No physical warp. All Chutes deloyed : Highest critical temp is airbrakes 1300K/2000K around 20km, then rapidly cooling down. No blowing up but chutes destroyed : crash.

I don't know what you did I didn't do, but I don't blow up.

Oh geez sorry, but you must have missed the last part of my prior post...

but my last test run was a success.

We are good.

[trash0551]

Hmmm, I'll check that too... I do the warp not to reduce heat but to save time !

I believe heat is calculated all the way through 1000x time warp. Since warp in atomsphere is just physics warp, it should be calculated there too (though with more floating point rounding errors).

I'd guess its not having the airbrakes open in space. Even at 69,999m, there is *some* atmosphere and so entering with airbrakes deployed is going to slow your (de)acceleration down. Over another 50km to 19km, that reduction in acceleration could be noticeable.

[Warzouz]

I rewrote the General flying section.

Ascent profile

- Don't activate SAS at take-off.

- Start gravity turn when speed is 40m/s. You should get to 45° at 8km.

- You may experience sliding during ascent : try to compensate or activate SAS.

- Orbit insertion burn should be from 300 to 600m/s.

- Wobbling payloads can wreck ascent. I suggest you use the "Kerbal Joints Reinforcement" mod created by Ferram4.

In space

- You should have 100 to 200m/s left before detaching the payload

- When on stable orbit, detach payload and stay on the SSTO stage.

- You should have a comfortable 200 to 500m/s of dV left for reentry.

- As the stage doesn't have any power generation, it will run out of power in few orbits.

Reentry

- I suggest a 60m/s deorbit on the west border of the crater (90° west of KSC). This means you would slighly overshoot KSC (70km)

- Follow retrograge if you want.

- Deploy airbrakes as soon as possible. If you forget, you'll destroy your chutes later and crash.

- Drogue chutes and regular chutes are configured to autodeploy at safe altitude (if you deploy airbrakes). Stage them as soon as possible (even in space)

- If you overshoot a lot, you can burn fuel, but keep at least 100m/s for powered landing. If you're too short, you can close airbrakes, but that's dangerous : you may not slow down enough to open you chutes safely.

- Drogues should deploy at 8km/5km (500m/s) and regular should open at 3km/800m (250m/s)

- At 100m, enable SAS to reduce rocket flip in water.

- Landing are powered : under 75m, tap "shift" once or twice to slow down around 5m/s.

- On touchdown or splashdown, keep SAS on and recover the stage as soon as possible. Don't let the rocket flip in water or fall on ground, that will break some expensive parts.

[Sharpy]

- if you see you'll undershoot and hit the mountains, switch the airbrakes off. There's still a plenty of time to slow down to a safe speed later - normally you achieve terminal velocity at some 12km altitude - you can safely begin the final braking from 1000m/s to "parachute speeds" at some 6km. And you can delay deployment of parachutes until some 600m altitude, just don't do it under phys-warp (deployment from "closed" to "fully extended" is such a rapid deceleration it can rip the rocket in half under phys-warp.)

- 100m/s for landing is a by far an overkill. Two notches up, 20m above touchdown will hardly burn more than 20m/s of delta-V. You really don't need to start the braking burn earlier as it takes under a second to slow down from the "unsafe" 10m/s to "safe" speeds. That means you can use the excess fuel for getting at a better landing spot.

I still don't have the big probe cores unlocked. So instead, I remove the one built in. Then I strip the decoupler and attach a fairing there, and a common probe core on top of it, then the payload on top of that. Since the rockets come in tail-down, it's occluded on reentry.

The most losses I get are from the rocket tipping over before I get to hit "recover".

[Warzouz]

- if you see you'll undershoot and hit the mountains, switch the airbrakes off. There's still a plenty of time to slow down to a safe speed later - normally you achieve terminal velocity at some 12km altitude - you can safely begin the final braking from 1000m/s to "parachute speeds" at some 6km. And you can delay deployment of parachutes until some 600m altitude, just don't do it under phys-warp (deployment from "closed" to "fully extended" is such a rapid deceleration it can rip the rocket in half under phys-warp.)

This is true for the lighter rockets, but for heavier rocket it may be dangerous. To have airbrakes make a difference, you have to close them for a long time. The best tim is to really make the 600m/s deorbit on the west ridge of the crater. You'll end 600km east of KSC in the sea. I tested a 70m/s deorbit on the same spot and ended in the moutains. Maybe 65m/s would land on KSC.

- 100m/s for landing is a by far an overkill. Two notches up, 20m above touchdown will hardly burn more than 20m/s of delta-V. You really don't need to start the braking burn earlier as it takes under a second to slow down from the "unsafe" 10m/s to "safe" speeds. That means you can use the excess fuel for getting at a better landing spot.

Sure, those are large safty limits.

I still don't have the big probe cores unlocked. So instead, I remove the one built in. Then I strip the decoupler and attach a fairing there, and a common probe core on top of it, then the payload on top of that. Since the rockets come in tail-down, it's occluded on reentry.

Nice. So you put the decoupler on top of you probe core ? Don't you get wobble from attaching a payload to a small node ?

The most losses I get are from the rocket tipping over before I get to hit "recover".

Yes, this is an issue with some of the rocket. Yesterday, I lost half a RR-15 in water because I miss clicked. As the rocket has fuel left, I could try adding 4 vernors near the top of the stage. They wouldn't be usefull to rotate the ship in space, but maybe they could help recover instable built.

[CloudlessEchoes]

Is there some trick to getting subassemblies to show up? I paste them in the folder but they don't show up in the list in the game. This has happened to me with other subassemblies in the past also.

Edit: ignore the above, I think I just don't have all the items needed in my career mode!

Edited September 6, 2015 by CloudlessEchoes

[Warzouz]

True, the design is quite endgame, especially with the large probe core (which is the same as the small, just heavier...)

[Warzouz]

I upgraded the package with the 400 tons and 600 tons launchers.

[drhay53]

Just wanted to say I've been using these for all of my launches the last few days, and so far, everything up to 150 tons of payload has been incredibly stable for me. These are extremely well-done.

I was wondering if you've thought about making a stable of lifters using SpaceY and KWRocketry engines? I'd just like to use them because they're cool. I don't know if you use them at all in your own save or anything.

Regardless, your lifters are my main go-to for getting anything to orbit. Thanks a (few hundred?) ton(s)!

[Warzouz]

Thanks. I spent quite few hours on those launchers, but now I can built nearly any variation my computer can handle in few minutes and be reasonably sure the rocket will go to LKO at first test.

I'm not into mods for now. I've lurked on MKS, but restart a stock game in 1.0. The concept if very basic it can be adapted to probably every mod.

As dV had reduced between beta 0.9 and 1.0 from 4500m/s to 3200m/s, SSTO rocket are much more viable. A regular staged launcher has around 25% mass efficiency. SSTO rocket are around 15/20%. As you recover the whole stage, I find the difference is not worth dealing wit staged launchers.

With the previous 4500m/s dV, the difference might have bee much less in favor of the SSTO rockets.

In other words : thos SSTO rocket may be too easy...

[SpaceplaneAddict]

Wait, 3200 M/S for SSTO rockets? YES! My ISRU SSTO rocket can get to Minmus!

[Warzouz]

Wait, 3200 M/S for SSTO rockets? YES! My ISRU SSTO rocket can get to Minmus!

Any rocket will need around 3200m/s (either SSTO or staged rockets). I put 3400m/s into my first stage when they need to be returned to ground.

If your payload is bulky or non streamlined, you may need more than 3200m/s. Also, if your TWR is too low, you'll need more dV (due to more gravity loss).

[CrashTestDanny]

Warzouz,

Not often do I bandy about the word perfect, but I just launched a 71t 2.5m x 5m cross-section (draggy as hell) payload on top of your RR-75, and there's no other way to describe the performance of your rocket.

After dropping my payload off at 79.8km, I had 219 dV left - perfect for immediate deorbit and landing 10km E of the pad.

Thanks!

Danny. And have some rep!

[Warzouz]

Hmmm, first 1.0.5 test :

- Airbrakes are much less useful, they burn very quickly. Maybe I'll remove them.

- Engines overheats on reentry (but no blow).

- Powered landing may not be as useful if splashing down (no damage at all at 12m/s, even flipping)

But that was successful.

[Warzouz]

OK after some more testing on the 300T launcher, things are quite complex.

I still recommend a very flat ascent path (try to cross 45° at 8000m). High path will need more fuel.

Deorbiting is still the same, but heating ins a real issue. On most of the rockets you won't blow you engines. But the 300T is heavy and has really littl drag. The Airbrakes have nearly no use and should be kept for less than 1200m slowdown, before drogues.

use engines to slowdown, but beware of keeping 100m/s for landing, even in water. As Mammoth would survive a splash at high speed, the tanks above won't.

I try adding some radiators, it didn't help saving the engines. But Rolling the rocket helps quite a lot. Small elevon could be added to the bottom wings to increase rolling (rolling will increase if elevon are reversed when SAS try to stop it)

Beware of auto deploy the chutes, the new aero and lack of airbrakes make chute deployment very near from the ground. Check chute color and deploy as soon as they change from red to yellow.

Also aim from sea, not shores, you might need the few meters...


NB : I successfully landed (with the help of MJ) the 300T stage with only the 2 drogue chutes after I destroyed the regular chutes.


Let's say the new heat management makes SSTO (rockets or planes) much harder than before.


Edit : A steeper descent (100m/s deorbit) a permanent rolling and a 250m/s burn help the airbrakes to stay open nearly all the time. I'll run some more tests. Please note the 300T is probably the hardest to land due to it's reentry high mass. Edited November 18, 2015 by Warzouz

[cephalo]

I've been using a modified version of your 100t lifter, and it has saved me a ton of cash and time lifting a bunch of big kerbodyne tanks to orbit. I put 8 drogues on there instead of 2, and I don't have to worry about retro-firing or having fuel left over for soft landings. I just have to come in shallow enough and it works. Thanks for this very instructive series of designs!

[Warzouz]

It's a long time since I did't do any update. I'm working on a 1.0.5 compatible Cygnus rocket series. My test subject is the RR300 variant (which is the heaviest I still use. As it's heavy it doesn't brake easily in atmosphere. I usually loose airbrakes, engines...

The new 1.0.5 version have the following changes.

• Replace wings with equivalent elevons
• Add action group to deactivate reaction wheels
• Removed all airbrakes
• Set drogue chutes to 8 items
• Remove all pressure config to chutes (no autodeploy anymore)

Reentry flight plan

• Deorbit 55m/s from the western border of the crater (90° west of KSC)
• Set to SAS to retrograde when entering in atmosphere
• Deactivate reactions wheels (the rocket should enter a chaotic rotation)
• Get ready to stage drogues as soon as the 500m/s is crossed
• Get ready to stage chutes as soon as the 250m/s is crossed
• You should he around 300m from the water around 30km from KSC...

Alternative flight plan (need 300m/s of fuel)

• Deorbit 60m/s from the western border of the crater (90° west of KSC)
• Set to SAS to retrograde when entering in atmosphere
• Roll the rocket when flames appear
• Watch for overheat of engines.
• Get ready to burn when overhead seems to be critical (but keep 100m/s)
• You should have much more time for drogues and chutes.

I'll update other variant and do more tests before posting the new pack.

• 
  

 

[Kerbal101]

Deorbit heat hangs together with:

- total weight to volume (for the lack of better term). Rocket full of fuel heats much higher than empty rocket (below).

- surfaces. more surfaces, less heat. I can only explain it, that object with low surface area tends to "sink" into atmosphere instead of gliding.

- total orbit. apoapsis at 200km is way hotter than 80km. I use controlled airbreaking at 55km. Controlled, because the periapsis altitude can be passively controlled by changing angle between retrograde and anti-radial/radial when nearing and passing it (effect flips in these stages). Its good to experiment on it from Mun orbit, set periapsis to 50km on Kerbin, SAS and watch what happens depending on angle.

- periapsis. periapsis at 30km is much colder, than 0km or even minus.

 

I had a bug recently, where I updated a bunch of mods, and all my rockets in space have been refuelled.

A re-entry at 15km P, 80km A  of my version of SSTO-R caused massive overheat and explosion to a big surprise.

But if I dumped the fuel or set orbit periapsis to 40 km, I landed safely.

The claim "faster you get below 35km, sooner you will cool" is totally false. The flatter the descend - less heat.

Also a good trick is to burn between retrograde and anti-radial (sky) - like 80 degree at anti-radial, this shifts the orbit forwards causing it to flatten. Burning towards radial, causes the opposite.

 

The airbrakes act similarly to retrograde burn (for free) -> they shorten the periapsis, increasing the angle, causing more heat and higher speed at surface.

But if your initial orbit had high periapsis (25km), then they will gradually slow down rocket - at same time increasing the angle.

For this reason, I don't think its a good idea to activate them above 20km - they will do more evil(angle increase) than good(speed reduction).

 

In my configurations, I use just the chutes. No drogue chutes. 1 chute per 4 tonne of *empty* rocket, typically between 8 and 32 chutes depending on rocket.

I never had to resort to airbreaks or powered descend.